Polymeric beads that are used in the separations industry are often based on either hydrophobic or hydrophilic monomers. One example of beads based on hydrophobic monomers are polystyrene-divinylbenzene (PS-DVB) beads that are useful hydrophobic separation materials, e.g. for reversed-phase chromatography or solid-phase extraction. An example of beads based on hydrophilic monomers are beads made from acrylamide and N,N′-methylenebisacrylamide that are useful hydrophilic separation materials, e.g. for size-exclusion chromatography.
The polymeric beads are most often produced by suspension polymerization where the monomer phase is not soluble in the continuous phase and instead forms droplets in the continuous phase. For example, styrene and divinylbenzene can be suspended in water using a propeller-type stirrer that disperses the monomer mixture, which often also contains a porogenic solvent and an initiator. Similarly, hydrophilic monomers can be dispersed in a non-polar continuous phase. For example, a solution of acrylamide, N,N′-methylenebisacrylamide and an initiator in water may be dispersed in mineral oil or an organic solvent such as chloroform. In both cases, a suitable surface active stabilizer may be added to facilitate the dispersion and stabilize the formed droplets. The polymerization reaction is initiated by heating and crosslinked polymer beads are obtained. This well known technique of suspension polymerization is widely used in the polymer industry to produce a wide range of polymer bead materials for use in a variety of separation processes.
In order to produce polymer beads with mixed chemistries, post-treatments of the polymer beads are known. Polystyrene-divinylbenzene beads may for example be treated with various chemicals to introduce ionic moieties or groups in the bead material and this is a common route for producing ion-exchange polymer bead materials. However, if ionic moieties or other very hydrophilic moieties are to be introduced directly into the beads by copolymerization during the suspension polymerization process, solubility issues may prevent the formation of the desired beads. If for example charged ionic monomers are mixed with hydrophobic monomers in a water-based suspension process, a copolymerization may not always occur as the monomers may partition into different phases of the two-phase system. This means that the desired copolymer will not be formed.
Reinholdsson et al (Reactive Polymers, Volume 17, Issue 2, May 1992, Pages 175-186) and Hargitai et al (Journal of Chromatography A, Volume 540, 1991, Pages 145-155 and Journal of Chromatography A, Volume 630, Issues 1-2, 5 Feb. 1993, Pages 79-94) disclose grafting of acryloyl chloride, methacryloyl chloride and (S)—N-acryloylphenylalanine ethyl ester onto poly(trimethylolpropane trimethacrylate) (TRIM) beads. The grafted polymer is not crosslinked and does not form its own network within the TRIM beads.
JP 59 202 210 discloses grafting of water-soluble monomers to polystyrene-divinylbenzene beads to give a grafted polymer bead. The polymer is useful for analysis of water-soluble polymers.
U.S. Pat. No. 7,119,145 discloses grafting of polystyrene-divinylbenzene copolymer beads with 1-vinyl-2-pyrrolidone to give a grafted polymer bead. The grafted polymer is not crosslinked and does not form its own network within the polystyrene/divinylbenzene beads. It further discloses a grafting method not affecting the morphology and physical structure of the polymer bead.
U.S. Pat. No. 5,882,521 discloses a copolymer of divinylbenzene and 1-vinyl-2-pyrrolidone. The polymer is produced in one step such that the monomers can be assumed to be randomly distributed throughout the polymer.
Even though a wide range of solid-phase separation materials are known, there are still separation applications where the existing materials do not have a desired combination of retention, selectivity and high recovery.
Consequently there is a need for solid-phase separation materials having improved separation characteristics. One object of the present invention is to provide a separation material having improved separations characteristics. One object is to provide a material for solid-phase separations such as solid-phase extraction (SPE) and chromatographic separations.